Determination of hydrogen ion concentrations in phosphate and borate mixtures by means of the quinhydrone electrodes.

THE application of the quinhydrone electrode (or the quinoquinhydrone electrode or the hydroquinhydrone electrode) as substitute for the hydrogen electrode for the determination of PH is based on the fact that the values of the potentials between one of these electrodes and the hydrogen electrode vary but very little if the electrolytes of the two electrodes of the chain examined are identical. For aqueous electrolytes at 180 the following values as a rule may be used: quinhydrone-hydrogen ... ... ... 0-7042 volt quinoquinhydrone-hydrogen ... .... 07562 hydroquinhydrone-hydrogen ... ... 0-6176 The potential shown above of the simple quinhydrone electrode being only valid for dilute solutions (up to 01-0-2 M), the constants of the quinoquinhydrone and hydroquinhydrone electrodes should also be valid at higher concentrations, and this has been verified by means of experiments [Biilmann, 1921, 1927; Biilmann and Lund, 1923]. As these electrodes are often applied in biological researches, it seems important to know how they act in phosphate and borate mixtures, and researches on these solvents have only been made with a simple quinhydrone electrode. In the following we shall first give the determinations of the fundamental potentials which may be used for the application of the different quinhydrone electrodes in phosphate and borate solutions. The solutions examined are: